The Jitter presented in PlexTools is automatically adjusted vertically as a completely relative measurement.
This means that it's impossible to know whether jitter is high or low - it's only possible to see how high/low jitter is on one part of the disc compared to jitter on another part of the disc.
Using the unofficial PxScan/PxView tools it's possible to see some "absolute" numbers for jitter, but those "absolute" numbers vary quite a lot between drives, so you cannot necessarily compare jitter values between scanning drives (even of the same model). You can however compare jitter on different discs scanned in the same drive.
The TA Jitter option is much better way to see absolute jitter values and compare between discs, although the values are not presented as a percentage.